1. Field of the Invention
This invention relates to a method for dissolving and degassing a polymer and a method for producing a porous film.
2. Description of Related Art
In the food industry, the medical industry, the electronic industry and so on, microfiltration films, ultrafiltration films, reverse-osmosis filtering films or the like that adopt porous films are used in most cases for the purpose of concentration, recycling useful ingredients, removing undesired ingredients, fresh water generation and so on. For the production of porous films, film-forming resins such as cellulose acetate, polyacrylonitrile, polysulfone, and fluorine-based resins are used.
As a method for producing a porous film, a method comprising the following steps has been known (e.g., Patent Documents 1 to 4).
Dissolution step: a step of dissolving a film-forming resin and a pore former in a solvent to obtain a film-forming starting solution.
Degassing step: a step of degassing the film-forming starting solution.
Solidification step: a step of discharging the degassed film-forming starting solution from a discharge means (e.g., a spinning nozzle, a T die or the like) and solidifying the same in a Solidification liquid to form a porous film.
In the dissolving step and the degassing step, dissolving the film-forming resin and the pore former sufficiently in the solvent and degassing the solution sufficiently have a significant influence on the quality of the porous film. However, if these steps take a long period of time, the solvent would evaporate to the environment and the quality of the film-forming starting solution would be degraded, and also the productivity would be decreased.